The proper control of an aircraft in all phases of its flight is based to a large extend upon the ability of the pilot to visually observe the terrain over which the aircraft is passing. In this regard, instrumentation, such as radar systems, and altimeters in combination with the use of accurate terrain maps aid the pilot in the flight of the aircraft; however, there are numerous conditions of flight which require actual observation of the terrain by the pilot to ensure proper navigation of the aircraft. For example, in cases of low altitude flying and landing of the aircraft under conditions which require quick reaction in the guiding of the aircraft over terrain which may provide rapidly changing contours and other obstacles to flight, the use of instruments alone is often unsatisfactory.
Accordingly, various systems have been proposed heretofore, including radar scanning systems and systems using preprocessed films of terrain over which an aircraft is to pass for providing to the pilot a display which simulates that which he would visualize if he were to actually view the terrain over which the aircraft is passing. One of the most recent developments in the area of moving map displays is a system for the dynamic display of terrain data which is stored as compressed data in digital form and which may be viewed on a cathode ray tube display in the form of a moving map that is automatically oriented under the control of the aircraft's navigational computer system to the instantaneous position of the aircraft with a heading-up disposition. Such a system is disclosed in copending U.S. application Ser. No. 224,742, filed Jan. 13, 1981, abandoned, and continued as Ser. No. 671,179, entitled "Digital Map Generator and Display System", in the name of Paul B. Beckwith, Jr., and assigned to the same assignee as the present application.
The system disclosed in the above-mentioned copending application provides a topographical two-dimensional real-time display of the terrain over which the aircraft is passing, and a slope-shading technique incorporated into the system provides to the display an apparent three-dimensional effect similar to that provided by a relief map. This is accomplished by reading compressed terrain data from a cassette tape in a controlled manner based on the instantaneous geographical location of the aircraft as provided by the aircraft navigational computer system, reconstructing the compressed data by suitable processing and writing the reconstructed data into a scene memory with a north-up orientation. A read control circuit then controls the read-out of data from the scene memory with a heading-up orientation to provide a real-time display of the terrain over which the aircraft is passing. A symbol at the center of display position depicts the location of the aircraft with respect to the terrain, permitting the pilot to navigate the aircraft even under conditions of poor visibility. However, the display provided by this system is in the form of a moving map rather than a true perspective display of the terrain as it would appear to the pilot through the window of the aircraft. Thus, the system disclosed in the copending application provides an arrangement for an indirect guidance of the aircraft over the terrain in that guidance is based upon the relative position of the symbol of the aircraft at the center of display position with respect to the moving map, rather than an arrangement for direct control of the aircraft with respect to the terrain on the basis of a three-dimensional display corresponding to the scene as it would actually appear to the pilot through the window of the aircraft.
Three-dimensional displays of terrain have been provided heretofore for aircraft guidance and flight simulation; however, such displays have been primarily simulated displays including only general characteristics of the terrain, such as an aircraft runway for aiding in aircraft landing and the like. Other systems for providing more detailed display of terrain data have been based on systems using preprocessed films of terrain. Unfortunately, such systems have not been entirely satisfactory in that they are often quite complex and are not capable of providing the detail insofar as elevation and cultural data is concerned which is required by the pilot of the aircraft for proper guidance. Such systems also are incapable of providing three-dimensional displays which correspond directly to a scene as might be observed through the window of the aircraft and, with the exception of the system disclosed in the above-mentioned copending Beckwith application, are incapable of providing a real-time display of terrain data taken into consideration changing altitude, heading and aircraft attitude.